You become "friends" with an ex on Facebook and reminisce about the past. You spend hours thinking about them and your heart races whenever you see a text from them. You tell yourself it's ok because you're not really cheating, you're just chatting. Biochemical research has shown that the effect of these love chemicals is twofold: they are released in response to your friend, and they bond you to him or her.

*Some names have been changed to protect the safety of the individuals involved. But in a cigarette-scented hotel room near a Chicago airport, more than a dozen men come and go with wet cheeks and quivering lips.